1. Field of the Invention
The invention relates to an optically readable record carrier comprising a radiation-sensitive layer upon a disc-shaped substrate and having an information recording area arranged in accordance with a spiral or concentric track pattern, which record carrier is intended for the recording and/or reproduction of information in the information recording area by means of a radiation beam, which track pattern exhibits a periodic modulation for the purpose of generating a clock signal for controlling the recording and/or reproducing process.
The invention further relates to an apparatus for manufacturing such a record carrier, comprising a writing device for writing the track pattern by means of a radiation beam and a control device for generating a periodic control signal for the writing device so as to modulate the track pattern at a frequency which corresponds to the frequency of the periodic control signal.
The invention further relates to an apparatus for recording information on such a record carrier, comprising means for scanning the tracks by means of a radiation beam, a modulation device for modulating the radiation beam intensity with an information signal, an optical system with a detector for detecting the radiation reflected or transmitted by the record carrier during scanning, and a device for deriving from the radiation detected by the detector a clock signal for controlling the recording apparatus.
The invention also relates to an apparatus for reading an information signal recorded on the information tracks of such a record carrier, comprising a scanning device for scanning the information tracks with a substantially constant velocity by means of a radiation beam, an optical system with a detector for detecting the radiation reflected or transmitted by the record carrier during scanning, a device for deriving from the detected radiation an information signal representing the recorded information, and a device for further deriving from the detected radiation a clock signal for controlling the reading apparatus.
2. Description of the Related Art
Such a record carrier and apparatus are described in German Offenlegungsschrift No. 3100421, which corresponds to pending U.S. application Ser. No. 110,063, assigned to the present assignee.
The known record carrier has a spiral track which exhibits a track modulation of constant frequency. As the spiral track is scanned by means of the radiation beam during reading and/or recording this track modulation produces a modulation of the reflected radiation beam. This modulation is detected and from the modulation thus detected a clock signal is derived which is utilized for controlling the recording and/or reading process.
Further, the spiral track is provided with information recording areas between which synchronisation areas are interposed. The information recording areas are intended for the recording of information. The synchronisation areas contain position information in the form of the address of the adjacent information recording area. The position information in the synchronization areas makes it possible to derive from the reflected radiation beam during scanning which part of the record carrier is being scanned. This enables a specific part of the disc to be located rapidly and accurately.
However, the known record carrier has the disadvantage that the information recording areas are constantly interrupted by synchronization areas. This is a drawback in particular when EFM-encoded information is to be recorded on the record carrier such because such recording of such information requires an uninterrupted information recording area. EFM-encoding is a method by which groups of 8 data bits at a time are translated into 14 channel bits for recording information on a compact digital disc. This is described, for example, in the article "Compact Disc: System Aspects and Modulation", Philips Tech. Rev. 40, No. 6, 1982.